Signaling



Sept. 27, 1938. w. KUMMERER ET AL ,4

SIGNALING Filed May 16, 1954 2 Sheets-Sheet 1 -F l29 I i INVENTORW/U/ELM mam/m5? 01/00 era-w ATTORNEY Sept. 27, 1938. w, KUMMERER ET AL2,131,443

SIGNALING 2 Sheets-Sheet 2 Filed May 16, 1934 CARR/67? W4l/E SOURCEO/RECT CURRENT SOURCE #LT g INVENTOR Mil/ELM lfl/MME/Pf/P ATTORNEYPatented Sept. 27, 1938 SIGNALING Wilhelm Kummerer and Rudolf Giirtler,Berlin,

Germany, assignors to Telefunken Gesellschaft' fiir DrahtlcseTelegraphic m. b. H., Berlin, Germany, a corporation of GermanyApplication May 16, 1934, Serial No. 725,846 In Germany May 18, 1933 10Claims.

This invention relates to an arrangement to change grid biasing voltagein tube circuits as a function of the signal strength.

In a great number of electric circuits comprising tubes it is desirablethat the static value of the voltage of a tube stage should adjustitself in a definite way as a function of the signal strength or anelectrical quantity controlled or governed thereby. The generalrequirement in cases like these is that in the presence of signalamplitudes falling below a certain minimum limit or level, the staticvalue of the voltage of a tube, say, the grid biasing voltage, shouldhave a selected constant, while being also constant and of higher valuein the presence of amplitudes above a definite upper limit. For signalamplitudes located midway between the said two limiting values, the saidbiasing voltage is to adjust itself as a function of the signalamplitude.

Now, according to this invention, control of the static voltage value tobe acted upon is insured by utilizing the fall of potential in aresistance caused by the plate direct current of an auxiliary tube,there being provided in the grid circuit of the said auxiliary tube anadditional resistance in series with a rectifier which is given anegative biasing voltage, across which additional resistance current ofthe rectifier controlled by the signal currents produces a potentialwhich is a function of the signal amplitude.

The novel features of the invention have been pointed out in the claimsattached hereto as required by law.

The nature of my invention and the operation thereof will be betterunderstood from the following detailed description thereof andtherefrom. when read in connection with the attached Fig. 3 is amodification of the arrangement of Fig. 2. In the arrangement of Fig. 3,the controlling potentials are derived from the modulating potentialsand the carrier wave amplitude is controlled by controlling the staticvoltage on the grid of the modulator in accordance with energycharacteristic of the modulating poten: tial amplitudes; while Figs. 4and 5 are modifications of a portion of the controlling circuits ofFigs. 1, 2. and 3.

The signal amplitude or else a voltage which is a function thereof, isimpressed upon the terminals I, 2, of the arrangement shown in Figure 1.By means of the rectifier 4 there is produced across the terminals ofcapacity 6 a'direct current voltage which isnegative with respect to thegrid of the tube 9-, the said direct current voltage acting, through itscontrol of the grid potential, upon the plate current of the tube 9flowing through the resistance Ill, thereby influencing the fall ofvoltage across the resistance NJ, to which generally a condenser II isconnected in parallel, and consequently across the terminals I4, 15. Thepotential drop across I4, I5, is caused to act in the grid circuitof theparticular stage whose grid biasing voltage is to be a function ofthesignal strength in a way as has hereinbefore been indicated. As ageneral rule, the grid circuit also contains in series with l4, l5, adirect current source IS. The static value of anode current of the tube9, apart from the direct current caused by the voltage of source l2, andthe plate resistance I0, is further a function of the size of thebiasing voltage of source 8. If desired, the source of biasing potential8 may be dispensed with.

In the case of all voltages across I, 2, whoseamplitude falls below apredetermined critical negative biasing potential of the rectifier 4 asadjusted at the source of direct current potential 5, the said rectifierwill be blocked so that no direct current voltage will arise across thecondenser 6. The grid bias is now supplied wholly by source 8. Theconsequence is that the working point of the tube will not be shifted bysignals of amplitude below said critical value, and .thus the voltageacross [0 remains constant. It is only in the presence of signalamplitudes which exceed the said lower critical value that the source 5is overcome so that the rectifier 4 becomes conductive; and there arisesacross the capacity 6 a potential which, according to its size,diminishes the plate current of tube 9 and thereby the fall of potentialacrossthe resistance 50 I0. In the presence of the selected criticalmaxi-- mum signal strength the direct current voltage arising at t is sohigh that. the tube 9 is out off or is blocked, no current flows-throughSand the potential drop across to will be -of.zero value. v

Signals which exceed the said upper limit will, to be sure, cause ahigher direct current voltage across the terminals of 6; but since thetube 9 is already blocked and the voltage at I4, I5 is zero, it followsthat the grid biasing voltage of the above mentioned tube connected toI4, I5 will not be altered by these signal potentials.

One practical application of the invention is illustrated in Figure 2.In this case the arrangement hereinbefore described serves the purposeto lessen the distortions occasioned by the curved portions of themodulation characteristic in a transmitter. The plate direct current oftube I8 is conducted by way of the resistance I3. The resistance I9which is traversed by the plate current of the auxiliary tube 9 isconnected in series with the source of voltage I6 andthe modulationtransformer I! in the grid circuit of the tube I9. The source I6 and/orresistance I I) shifts the working point of the tube I9 into thelowerportion of its characteristic curve so that the tube is working in theregion of and above the lower knee. In lieu of the voltage sources 5 and8 of Figure 1, the biasing voltage 5a is provided in the circuit schemeof Figure 2. The resistance Ia as a general rule is high compared withthe resistance I3 and the internal resistance of the valve 4. By theplate current of the tube 9 an additional biasing voltage for the tubeI9 is occasioned across the external resistance II]. Inasmuch as theplate direct current of the tube I8 grows with the amplitude of thealternating current amplitude or the percentage of modulation, it willbe seen that also the potential across the resistance I3 will increase.If then, in the course of operation of the modulator circuit theadmissible modulation percentage is extended or increased so that thewave amplitudes grow to such degree that they extend as far as the lowerknee of the characteristic curve. of tube I8, there is produced a growthof the plate current of the tube I8 and also due to the saidrectification in tube I8 the same is negatively biased to acorresponding degree. Due to increase in plate current in I8 the fall ofpotential across the resistance I3 in the plate-to-cathode circuit of I8also grows. Past a certain point, the potential drop across resistanceI3 will exceed the electromotive force produced by source 5a and therectifier 4 will become conductive. This permits the negative biasingvoltage produced across resistance I3 to reach the grid of tube 9.Consequently, the plate current through 9 and the voltage produced bythe potential drop across the resistance I0 are both diminished. Theresultant biasing voltage of the tube I9 becomes less negative and theworking point of tube I9 climbs up along the characteristic curve. Aworking point located above the lower bend at closer proximity to themiddle of the characteristic curve results in 'a greater freedom fromdistortion. My novel circuit insures operation of the tube I9 at suchworking point. The arrangement is so dimensioned in this instance thatthe valve 4 remains blocked as long as the operation takes placesomewhere above the lower bend of the characteristic curve upon therectilinear part of the modulation characteristic. And for the samelength of time, also the grid biasing voltage will remain constant inthe tube I9. In other words this modulation percentage is exceeded withthe result that operation takes place in the curved portion of themodulation characteristic,,then the fall of potential across I3 will gobeyond and exceed the biasing voltage 5a, the valve 4 becomes conductingand the higher voltage from I3 will reach and become active at the gridof tube 9, with the result that the plate current decreases andtherewith the fall of potential across Ill and thus the biasing voltageof the tube I9. As a result the latter will be modulated to a higherdegree or percentage, as the alternating current amplitude grows, andthe modulation characteristic of the tube I9 becomes straighter. Inother words, inside certain limits a correction of the distortion isbrought about. By choosing dimensions appropriately, conditions may beso made that in the presence of modulation the tube 9 will just beblocked. In that case the fall of voltage across I0 becomes zero, .andthe biasing voltage of the tube I9 can not be changed any further. Whenthe plate current in I8 assumes larger values, this will cause noadditional efiect upon the tube I 9 because the lower negative biasingvoltage of I9 is limited by the source I6.

Another exemplified embodiment of the basic idea of the invention isillustrated in Figure 3. This is the fundamental scheme of themodulation stage of a transmitter of the thermionictube type whosecarrier is controlled or modulated in proportion to the signal strength.For the purpose of insuring carrier control recourse is hadfundamentally to a scheme of the kind shown in Figure 1 which in thepresent instance is somewhat expanded and developed for the sake ofexample. The signal voltage is impressed upon the terminals I and 2, andon the transformer I'I. When the amplitude of the signal voltage is at alow critical value, or below, rectifier 4 is blocked by the source 5 andthe bias potential on the grid of 9 is due substantially solely to thevoltage of Ba as modified by resistors 20, etc., and 9 is conductive.Plate current flowing through 9 and through resistance I9 produces apotential drop in ID. The potential drop in II] adds to the voltage ofsource I6, as in Figure l, and the plate current through I9 falls. Now,if the modulating voltage amplitude equals a critical value, or more,the rectifier valve 4 becomes conductive and current flows in theresistance I producing a voltage drop which modifies the potentialsupplied from 8a to bias the grid of 9 more negative, thereby lowering9s conductivity and reducing the flow of current through ID. This makesthe control grid of I9 less negative and increases the flow of platecurrent in I9. In this manner we produce across the resistance II] afall of potential which is a function of the signal strength. The sizeof the capacities 6 and II and of the resistances I and I0 govern theparticular rate of speed at which the direct current voltage across I4,I 5, will increase and diminish. Contradistinct to known circuit schemesused for the control of the carrier wave, it is possible in the presentinvention to adjust to a large extent the speed of carrier growthregardless and independently of the rate of speed of the reduction ofthe carrier. If the ripples of the direct current voltage across I 4, I5can not be suificiently suppressed or smoothed by the capacities 6 andII seeing that the values of the latter can not be raised ad libitumbecause of the resultant time-constants, it would be recommendable touse filter circuits of the kind as shown, for instance, in Figure 3where instead of 6 the filter circuit 6, 2|, 22 is connected.

. Figure 3 shows a further development of the arrangement residing inthe provision of the resistance 29 which is traversed by the platecurrent of tube 9 and which is included in the grid circuit of the tube9, said resistance serving the purpose of compensating the curvature ofthe characteristic of the tube 9. The said resistance will have to beused whenever the desideratum is to insure as linear as feasible aninterrelationship between the signal amplitude across I and 2, and thebiasing voltage across M and I5.

Cases may arise in which the voltage across the resistance I0 is notdesired to bear a linear dependence upon the signal amplitude. In thatinstance, at the point marked 9 one or more tubes possessing suitablecharacteristics are provided. Also the frequency curve of thetransformer 3 may be so chosen that between the signal amplitude acrossI, 2, and the voltage across l4, it, the desired non-linear relationshipwill be fulfilled.

The lower and the upper limit or levels depend upon the choice of therectifier bias, in Figures 1 and 3, and the turn-ratio of thetransformer 3 or the adjustment of the potentiometer l3, in Figure 3.Hence, what is essential is that the voltage at 5 and in some suitablemanner also the ratio of transformation of the applied voltage and theone transferred to the rectifier should be adjustable.

If an extensive suppression of the voltage ripples is desired, then asillustrated in Figure 4, two tubes 9, 9a, are connected push-pullfashion in the grid, while their plates are connected in parallel. Therectifier 4 works upon the capacity 6 and the resistance 1 in the gridcircuit of the tube 9 and upon the capacity 60. and the resistance la.in the grid circuit of the tube 9a. The voltage ripples across to are ofopposite phase compared with the voltage ripples across 5 so that theywill largely be neutralized at the plate end. The condenser l I may bechosen so small that it will practically exercise no effect upon thetime constant under certain circumstances it may be dispensed with. Sofar as the dimensioning of the condensers 6 and 6a and of theresistances 7, la, are concerned there is a good deal of latitude in thecase of this circuit scheme.

When using tubes having their grids connected push-pull fashion therectifier 4 may be dispensed with, while the grid biasing Voltage of thetubes 9, 9a, which is to be a function of thesignal may be obtained bymeans of grid rectification. One exemplified embodiment of such anarrangement is schematically shown in Figure 5. By selection of thebiasing potential 5 and adjustment of the potentiometer E3, the upperand the lower control limits or levels are fixed.

Having thus described my invention and the operation thereof, what Iclaim is:

1. A signaling system comprising, a thermionic tube having a controlgrid and a cathode, a circuit for applying carrier waves to said controlgrid, a source of modulating potentials, a transformer having itsprimary winding connected to said source of modulating potentials, aresistance and a source of potential connecting the secondary winding ofsaid transformer between the control grid and cathode of said firstnamed tube, a rectifier having its input electrodes energized by saidmodulating potentials, an additional tube having an anode, a cathode anda control grid, a second resistance, a filter circuit connecting theoutput electrodes of said rectifier in parallel with said secondresistance, a connection between said second resistance and the controlgrid and cathode of said additional tube, and a connection between theanode and cathode of said additional tube and said first namedresistance.

2. In a signaling system, an electron discharge device having acontrolling electrode and a cathode, a circuit applying carrier waveenergy to said controlling electrode, a source of modulating potentials,an impedance and a source of direct current potential connecting saidsource of modulating potentials between the controlling electrode andcathode of said first named device, a rectiher having input electrodesenergized by said modulating potentials, an additionaltube having ananode, a cathode, and a controlling electrode, a second impedance, afilter circuit connecting the output electrodes of said rectifier withsaid second impedance, a connection between said second named impedanceand the controlling electrode and cathode of said additional tube, and aconnection between the anode and cathode of said additional tube andsaid first named impedance. 7

3. In a modulation system, an electron discharge modulating devicehaving electrodes ineluding input electrodes on which wave energy to bemodulated is impressed, a source of modulating potentials connected withan electrode in said device and means to regulate the static value ofthe operating voltages of said device as a func tion of the strength ofsaid modulating potentials comprising, an auxiliary'tube having ananode, a cathode and a control grid, at resistance connected between theanode and cathode of said auxiliary tube, a capacity connected inparallel with said resistance, said capacity being suitable to thefrequency of said modulating potentials, means for coupling saidresistance to an electrode in said discharge device, the voltage appliedto which is to be regulated, a second resistance and a rectifier and asource of direct current potential in series connected with the controlgrid and cathode of said auxiliary tube, said source of potential beingof such avalue and so connected as to normally block said rectifier,means for biasing the control grid of said auxiliary tube relative toits cathode by a potential such that current normally flows in saidauxiliary tube and first resistance, and a circuit for ap-'- plyingenergy characteristic of the modulating potentials to the inputelectrodes of said rectifier for overcoming said blocking potential whenthe amplitude of the modulating potentials exceeds a selected value.

4. A system as recited in claim 3 in which said second resistanceconnected with the control grid and cathode of said auxiliary tube isconnected with said rectifier by way of a filtering circuit comprisingcapacity.

5. In a modulation system, an electron discharge modulating devicehaving electrodes including input electrodes on which wave energy to bemodulated is impressed, a source of modulating potentials connected withan electrode in said device and means to regulate the static value ofthe operating voltages of said device as a function of the strength ofsaid modulating potentials comprising, a pair of auxiliary tubes eachhaving an anode, a cathode and a control grid, a resistance connectedbetween the anodes and cathodes of said auxiliary tubes, a capacityconnected in parallel with said resistance, said capacity being suitableto the frequency of said modulating potentials, means for coupling saidresistance to an electrode in said discharge device, the voltage appliedto which is to be regulated, a rectifier and a source of direct currentpotential in series connected with the control grid and .cathode of eachof said auxiliary tubes, said source of direct current potential beingof such a value and so connected as to normally block said rectifier,means for biasing said auxiliary tubes by potentials such that currentnormally flows in said auxiliary tubes and first resistance, and acircuit for applying energy characteristic of the modulating potentialsto the input electrodes of ,said rectifier for overcoming said blockingpotential when the amplitude of the'modulating potentials exceeds aselected value.

6. In a modulating system an electron discharge modulating device havingelectrodes including input electrodes on which wave energy to bemodulated is impressed, a source of modulating potentials connected withan electrode in said device and means to regulate the static value ofthe operating voltage applied to an electrode of said device as afunction of the strength of the modulating potentials comprising a pairof auxiliary thermionic tubes each having an anode, a cathode and acontrol grid, a resistance connecting the anodes and cathodes of saidauxiliary tubes in parallel relation, a circuit for coupling saidresistance to an electrode in said modulating device, a circuitconnected between the control grids of said auxiliary tubes, means forcoupling said circuit to said source of modulating potentials, arectifier connecting a point on said circuit between the control gridsof said auxiliary tubes to the cathodes of said auxiliary tubes, andmeans connected with said rectifier for normally blocking saidrectifier.

'7. An arrangement as recited in claim 6 in which the control grid andcathode of each of said auxiliary tubes is shunted by a resistance andby a condenser and in which direct current potentials are applied to theanodes of said auxiliary tubes to charge the said anodes relative to thecathodes by potentials such that said auxiliary tubes are conductive inthe absence of signals to be amplified.

8. In a modulation system a thermionic modulator tube having electrodesincluding a control grid and cathode, a source of wave energy to bemodulated and a source of modulating potentials coupled to said controlgrid and cathode and means to regulate the static value of the biasingpotential applied to the control grid of said thermionic modulator tubeas a function of the strength of the modulating potentials comprising,an auxiliary tube having an anode, a cathode and a control grid, aresistance connected between the anode and cathode of said auxiliarytube, means for biasing said control grid of said auxiliary tuberelative to its cathode by a potential such that current flows in saidtube and resistance to produce in said resistance a potential drop, asource of potential coupling said resistance to the control grid andcathode of said modulator tube to apply therebetween said potential dropand potential from said source of potential, a rectifier having itsanode circuit connected to the control grid of said auxiliary tube, saidrectifier being normally biased to cut off, and means for applyingmoduated wave energy from said first tube to the input electrodes ofsaid rectifier to control the conductivity thereof.

9. In a modulating system, an electron discharge modulator device havinga control electrode and a cathode and an output electrode from whichmodulated energy is derived, a source of wave energy coupled to saidcontrol electrode, a source of signal voltage coupled to an electrode insaid device, and means to regulate the static value of the operatingvoltage applied to the control electrode of said electron dischargedevice as a function of the amplitude of the signal voltage to beimpressed on an electrode of said device and to limit said regulatingaction between upper and lower voltage amplitudes comprising a source ofbiasing potential and an impedance for applying to said controlelectrode relative to said cathode of said device a selected biasingpotential, means for changing said biasing potential when the amplitudeof said signal voltage exceeds a selected critical lower valuecommensurate with said selected biasing potential, said last named meanscomprising an additional discharge device having output electrodesconnected to said impedance and having input electrodes, a rectifierhaving an output connected to the input electrodes of said additionaldischarge device and an input excited by voltages characteristic of saidsignal voltages, and means for normally biasing said rectifier to outoff in the presence of signal voltages equal to or lower than saidselected critical value.

10. A system as recited in claim 9 including means for rendering saidmeans for changing said selected biasing potential inoperative when saidvoltages characteristic of signal voltages exceed a predetermined upperamplitude value whereby the biasing potential on said control electrodeof said first discharge device is controlled in accordance with theamplitude of said voltages characteristic of signals between said upperand lower limits.

WILHELM KUMMIERER. RUDOLF GI'JRTLER.

